Method for palette mode coding

ABSTRACT

A method for decoding video data provided in a bitstream, where the bitstream includes a coding unit (CU) coded in palette mode, includes: parsing a palette associated with the CU provided in the bitstream; parsing one or more run lengths provided in the bitstream that are associated with the CU; parsing one or more index values provided in the bitstream that associated with the CU; and parsing one or more escape pixel values provided in the bitstream that are associated with the CU. The escape pixel values may be parsed from consecutive positions in the bitstream, the consecutive positions being in the bitstream after all of the run lengths and the index values associated with the CU. The method may further include decoding the CU based on the parsed palette, parsed run lengths, parsed index values, and parsed escape values.

INCORPORATION BY REFERENCE TO PRIORITY APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.62/020,340, filed Jul. 2, 2014 and U.S. Provisional Application No.62/028,039, filed Jul. 23, 2014.

TECHNICAL FIELD

This disclosure relates to the field of video coding and compression,and particularly to screen content coding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, digital cameras, digital recording devices,digital media players, video gaming devices, video game consoles,cellular or satellite radio telephones, video teleconferencing devices,and the like. Digital video devices implement video compressiontechniques, such as those described in the standards defined by MovingPicture Experts Group-2 (MPEG-2), MPEG-4, International Telegraph UnionTelecommunication Standardization Sector (ITU-T) H.263, ITU-TH.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High EfficiencyVideo Coding (HEVC) standard, and extensions of such standards. Thevideo devices may transmit, receive, encode, decode, and/or storedigital video information more efficiently by implementing such videocoding techniques.

With the prevalence of high speed Internet access, emerging videoapplications such as remote desktop sharing, virtual desktopinfrastructure, and wireless display require high compression efficiencyof screen contents. However, additional intra and inter video codingtools were designed primarily for natural contents. Screen contents havesignificantly different characteristics compared with natural contents(e.g., sharp edges and less or no noise), which makes those traditionalcoding tools less sufficient.

SUMMARY

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

In one aspect, a method of decoding video data in a bitstream, where thebitstream includes a coding unit (CU) coded in palette mode, includes:parsing a palette associated with the CU provided in the bitstream, thepalette including a plurality of palette entries that are eachassociated with an index value and a pixel value associated with theindex value; parsing one or more run lengths provided in the bitstreamthat are associated with the CU, each run length indicating a number ofconsecutive positions, starting from and including a current position inthe CU, that are associated with a copy-left mode or a copy-above mode;parsing one or more index values provided in the bitstream thatassociated with the CU, each index value indicating a pixel value in thepalette that is associated with the current position in the CU; parsingone or more escape pixel values provided in the bitstream that areassociated with the CU, each escape pixel value indicating a pixel valuethat is not in the palette, wherein the escape pixel values are parsedfrom consecutive positions in the bitstream, the consecutive positionsbeing in the bitstream after all of the run lengths and the index valuesassociated with the CU; and decoding the CU based on the parsed palette,parsed run lengths, parsed index values, and parsed escape values.

In another aspect, an apparatus for decoding video data provided in abitstream includes a memory and a processor in communication with thememory. The memory is configured to store video data associated with thebitstream, the bitstream including a coding unit (CU) coded in palettemode. The processor is configured to: parse a palette associated withthe CU provided in the bitstream, the palette including a plurality ofpalette entries that are each associated with an index value and a pixelvalue associated with the index value; parse one or more run lengthsprovided in the bitstream that are associated with the CU, each runlength indicating a number of consecutive positions, starting from andincluding a current position in the CU, that are associated with acopy-left mode or a copy-above mode; parse one or more index valuesprovided in the bitstream that associated with the CU, each index valueindicating a pixel value in the palette that is associated with thecurrent position in the CU; parse one or more escape pixel valuesprovided in the bitstream that are associated with the CU, each escapepixel value indicating a pixel value that is not in the palette, whereinthe escape pixel values are parsed from consecutive positions in thebitstream, the consecutive positions being in the bitstream after all ofthe run lengths and the index values associated with the CU; and decodethe CU based on the parsed palette, parsed run lengths, parsed indexvalues, and parsed escape values.

In one aspect, a method of encoding video data in a bitstream includes:analyzing a plurality of pixels in a coding unit (CU), each pixel havinga pixel value associated therewith; generating a palette based on theplurality of pixels in the CU, the palette including a plurality ofpalette entries that are each associated with an index value and a pixelvalue associated with the index value; determining one or more runlengths associated with the CU in the bitstream, each run lengthindicating a number of consecutive positions, starting from andincluding a current position in the CU, that are associated with acopy-left mode or a copy-above mode; determining one or more indexvalues associated with the CU in the bitstream, each index valueindicating a pixel value in the palette that is associated with thecurrent position in the CU; determining one or more escape pixel valuesassociated with the CU in the bitstream, each escape pixel valueindicating a pixel value that is not in the palette; and encoding the CUbased on the generated palette, determined run lengths, determined indexvalues, and determined escape pixel values, wherein the escape pixelvalues are encoded in consecutive positions in the bitstream, theconsecutive positions being in the bitstream after all of the runlengths and the index values associated with the CU.

In another aspect, an apparatus for encoding video data in a bitstreamincludes a memory and a processor in communication with the memory. Thememory is configured to store video data associated with the bitstream,the bitstream including a coding unit (CU) coded in palette mode. Theprocessor is configured to: analyze a plurality of pixels in a codingunit (CU), each pixel having a pixel value associated therewith;generate a palette based on the plurality of pixels in the CU, thepalette including a plurality of palette entries that are eachassociated with an index value and a pixel value associated with theindex value; determine one or more run lengths associated with the CU inthe bitstream, each run length indicating a number of consecutivepositions, starting from and including a current position in the CU,that are associated with a copy-left mode or a copy-above mode;determine one or more index values associated with the CU in thebitstream, each index value indicating a pixel value in the palette thatis associated with the current position in the CU; determine one or moreescape pixel values associated with the CU in the bitstream, each escapepixel value indicating a pixel value that is not in the palette; andencode the CU based on the generated palette, determined run lengths,determined index values, and determined escape pixel values, wherein theescape pixel values are encoded in consecutive positions in thebitstream, the consecutive positions being in the bitstream after all ofthe run lengths and the index values associated with the CU.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 1B is a block diagram illustrating another example video encodingand decoding system that may perform techniques in accordance withaspects described in this disclosure.

FIG. 2 is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3 is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 is a block diagram illustrating an input CU, an index block, anescape pixel, and a palette associated with the CU.

FIG. 5 is a flowchart illustrating a method for coding video data in abitstream in accordance with aspects described in this disclosure.

FIG. 6 is a flowchart illustrating a method for decoding video data in abitstream in accordance with aspects described in this disclosure.

FIG. 7 is a flowchart illustrating another method for decoding videodata in a bitstream in accordance with aspects described in thisdisclosure.

FIG. 8 is a flowchart illustrating another method for coding video datain a bitstream in accordance with aspects described in this disclosure.

FIG. 9 is a flowchart illustrating a method for encoding video data in abitstream in accordance with aspects described in this disclosure.

DETAILED DESCRIPTION

In existing implementations of screen content coding, there may be someredundancies in the bitstream. These redundancies may be removed byskipping certain syntax element signaling when certain conditions aresatisfied. In addition, some syntax elements may introduce parsingdependency. For example, a syntax element for indicating the run modemay not need to be signaled if the current pixel is in the first line ofthe block, since the decoder may infer the run mode to be index copymode (e.g., copy left mode). In addition, in a case where the decoderdecodes the index value first, and depending on the decoded index value,the decoder decides whether the mode is index copy mode or escape mode(e.g., based on whether or not the index value represents an escapeindex value). If the decoder determines the mode to be index copy mode,the decoder parser continues to parse run length. If the decoderdetermines the mode to be escape mode, the decoder parser may continueto parse escape values and/or run length. Since parsers usually operateat a much higher speed than decoders, such dependency between decodingengine and parsing engine may affect parser's throughput (e.g., sincethe parsing engine may need to wait for the decoding engine to decodethe parsed bits). Thus, an improved method of processing blocks coded inpalette coding mode is desired. In this application, several novelmethods for organizing the palette elements in the bitstream to avoid orreduce the parsing dependency in palette mode are described.

In the description below, H.264/Advanced Video Coding (AVC) techniquesrelated to certain embodiments are described; the HEVC standard andrelated techniques are also discussed. While certain embodiments aredescribed herein in the context of the HEVC and/or H.264 standards, onehaving ordinary skill in the art would appreciate that systems andmethods disclosed herein may be applicable to any suitable video codingstandard. For example, embodiments disclosed herein may be applicable toone or more of the following standards: International TelecommunicationUnion (ITU) Telecommunication Standardization Sector (ITU-T) H.261,International Organization for Standardization/InternationalElectrotechnical Commission (ISO/IEC) MPEG-1 Visual, ITU-T H.262 orISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-TH.264 (also known as ISO/IEC MPEG-4 AVC), including the range extension.

HEVC generally follows the framework of previous video coding standardsin many respects. The unit of prediction in HEVC is different fiom theunits of prediction (e.g., macroblocks) in certain previous video codingstandards. In fact, the concept of a macroblock does not exist in HEVCas understood in certain previous video coding standards. A macroblockis replaced by a hierarchical structure based on a quadtree scheme,which may provide high flexibility, among other possible benefits. Forexample, within the HEVC scheme, three types of blocks, Coding Unit(CU), Prediction Unit (PU), and Transform Unit (TU), are defined. CU mayrefer to the basic unit of region splitting. CU may be consideredanalogous to the concept of macroblock, but HEVC does not restrict themaximum size of CUs and may allow recursive splitting into four equalsize CUs to improve the content adaptivity. PU may be considered thebasic unit of inter/intra prediction, and a single PU may containmultiple arbitrary shape partitions to effectively code irregular imagepatterns. TU may be considered the basic unit of transform. TU can bedefined independently from the PU; however, the size of a TU may belimited to the size of the CU to which the TU belongs. This separationof the block structure into three different concepts may allow each unitto be optimized according to the respective role of the unit, which mayresult in improved coding efficiency.

Video Coding Standards

A digital image, such as a video image, a TV image, a still image or animage generated by a video recorder or a computer, may include pixels orsamples arranged in horizontal and vertical lines. The number of pixelsin a single image is typically in the tens of thousands. Each pixeltypically contains luminance and chrominance information. Withoutcompression, the sheer quantity of information to be conveyed from animage encoder to an image decoder would render real-time imagetransmission impractical. To reduce the amount of information to betransmitted, a number of different compression methods, such as JPEG,MPEG and H.263 standards, have been developed.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), and HEVC including therange extension.

In addition, a video coding standard, namely HEVC, has been developed bythe Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T VideoCoding Experts Group (VCEG) and ISO/IEC MPEG. The full citation for theHEVC Draft 10 is document JCTVC-L1003, Bross et al., “High EfficiencyVideo Coding (HEVC) Text Specification Draft 10,” Joint CollaborativeTeam on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG11, 12th Meeting: Geneva, Switzerland, Jan. 14, 2013 to Jan.23, 2013. The range extension to HEVC is also being developed by theJCT-VC.

Video Coding System

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the present disclosure. For example, an apparatus may be implementedor a method may be practiced using any number of the aspects set forthherein. In addition, the scope of the present disclosure is intended tocover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the present disclosure set forthherein. It should be understood that any aspect disclosed herein may beembodied by one or more elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The attached drawings illustrate examples. Elements indicated byreference numbers in the attached drawings correspond to elementsindicated by like reference numbers in the following description. Inthis disclosure, elements having names that start with ordinal words(e.g., “first.” “second,” “third,” and so on) do not necessarily implythat the elements have a particular order. Rather, such ordinal wordsare merely used to refer to different elements of a same or similartype.

FIG. 1A is a block diagram that illustrates an example video codingsystem 10 that may utilize techniques in accordance with aspectsdescribed in this disclosure. As used described herein, the term “videocoder” or “coder” refers generically to both video encoders and videodecoders. In this disclosure, the terms “video coding” or “coding” mayrefer generically to video encoding and video decoding. In addition tovideo encoders and video decoders, the aspects described in the presentapplication may be extended to other related devices such as transcoders(e.g., devices that can decode a bitstream and re-encode anotherbitstream) and middleboxes (e.g., devices that can modify, transform,and/or otherwise manipulate a bitstream).

As shown in FIG. 1A, video coding system 10 includes a source device 12that generates encoded video data to be decoded at a later time by adestination device 14. In the example of FIG. 1A, the source device 12and destination device 14 constitute separate devices. It is noted,however, that the source device 12 and destination device 14 may be onor part of the same device, as shown in the example of FIG. 1B.

With reference once again, to FIG. 1A, the source device 12 and thedestination device 14 may respectively comprise any of a wide range ofdevices, including desktop computers, notebook (e.g., laptop) computers,tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, or the like. In various embodiments, the source device 12 andthe destination device 14 may be equipped for wireless communication.

The destination device 14 may receive, via link 16, the encoded videodata to be decoded. The link 16 may comprise any type of medium ordevice capable of moving the encoded video data from the source device12 to the destination device 14. In the example of FIG. 1A, the link 16may comprise a communication medium to enable the source device 12 totransmit encoded video data to the destination device 14 in real-time.The encoded video data may be modulated according to a communicationstandard, such as a wireless communication protocol, and transmitted tothe destination device 14. The communication medium may comprise anywireless or wired communication medium, such as a radio frequency (RF)spectrum or one or more physical transmission lines. The communicationmedium may form part of a packet-based network, such as a local areanetwork, a wide-area network, or a global network such as the Internet.The communication medium may include routers, switches, base stations,or any other equipment that may be useful to facilitate communicationfrom the source device 12 to the destination device 14.

Alternatively, encoded data may be output from an output interface 22 toa storage device 31 (optionally present). Similarly, encoded data may beaccessed from the storage device 31 by an input interface 28, forexample, of the destination device 14. The storage device 31 may includeany of a variety of distributed or locally accessed data storage mediasuch as a hard drive, flash memory, volatile or non-volatile memory, orany other suitable digital storage media for storing encoded video data.In a further example, the storage device 31 may correspond to a fileserver or another intermediate storage device that may hold the encodedvideo generated by the source device 12. The destination device 14 mayaccess stored video data from the storage device 31 via streaming ordownload. The file server may be any type of server capable of storingencoded video data and transmitting that encoded video data to thedestination device 14. Example file servers include a web server (e.g.,for a website), a File Transfer Protocol (FTP) server, network attachedstorage (NAS) devices, or a local disk drive. The destination device 14may access the encoded video data through any standard data connection,including an Internet connection. This may include a wireless channel(e.g., a wireless local area network (WLAN) connection), a wiredconnection (e.g., a digital subscriber line (DSL), a cable modem, etc.),or a combination of both that is suitable for accessing encoded videodata stored on a file server. The transmission of encoded video datafrom the storage device 31 may be a streaming transmission, a downloadtransmission, or a combination of both.

The techniques of this disclosure are not limited to wirelessapplications or settings. The techniques may be applied to video codingin support of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, streaming video transmissions, e.g.,via the Internet (e.g., dynamic adaptive streaming over HypertextTransfer Protocol (HTTP), etc.), encoding of digital video for storageon a data storage medium, decoding of digital video stored on a datastorage medium, or other applications. In some examples, video codingsystem 10 may be configured to support one-way or two-way videotransmission to support applications such as video streaming, videoplayback, video broadcasting, and/or video telephony.

In the example of FIG. 1A, the source device 12 includes a video source18, video encoder 20 and the output interface 22. In some cases, theoutput interface 22 may include a modulator/demodulator (modem) and/or atransmitter. In the source device 12, the video source 18 may include asource such as a video capture device, e.g., a video camera, a videoarchive containing previously captured video, a video feed interface toreceive video from a video content provider, and/or a computer graphicssystem for generating computer graphics data as the source video, or acombination of such sources. As one example, if the video source 18 is avideo camera, the source device 12 and the destination device 14 mayform so-called “camera phones” or “video phones”, as illustrated in theexample of FIG. 1B. However, the techniques described in this disclosuremay be applicable to video coding in general, and may be applied towireless and/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby the video encoder 20. The encoded video data may be transmitted tothe destination device 14 via the output interface 22 of the sourcedevice 12. The encoded video data may also (or alternatively) be storedonto the storage device 31 for later access by the destination device 14or other devices, for decoding and/or playback. The video encoder 20illustrated in FIGS. 1A and 1B may comprise the video encoder 20illustrated FIG. 2 or any other video encoder described herein.

In the example of FIG. 1A, the destination device 14 includes the inputinterface 28, a video decoder 30, and a display device 32. In somecases, the input interface 28 may include a receiver and/or a modem. Theinput interface 28 of the destination device 14 may receive the encodedvideo data over the link 16 and/or from the storage device 31. Theencoded video data communicated over the link 16, or provided on thestorage device 31, may include a variety of syntax elements generated bythe video encoder 20 for use by a video decoder, such as the videodecoder 30, in decoding the video data. Such syntax elements may beincluded with the encoded video data transmitted on a communicationmedium, stored on a storage medium, or stored a file server. The videodecoder 30 illustrated in FIGS. 1A and 1B may comprise the video decoder30 illustrated FIG. 3 or any other video decoder described herein.

The display device 32 may be integrated with, or external to, thedestination device 14. In some examples, the destination device 14 mayinclude an integrated display device and also be configured to interfacewith an external display device. In other examples, the destinationdevice 14 may be a display device. In general, the display device 32displays the decoded video data to a user, and may comprise any of avariety of display devices such as a liquid crystal display (LCD), aplasma display, an organic light emitting diode (OLED) display, oranother type of display device.

In related aspects, FIG. 1B shows an example video coding system 10′wherein the source device 12 and the destination device 14 are on orpart of a device 11. The device 11 may be a telephone handset, such as a“smart” phone or the like. The device 11 may include acontroller/processor device 13 (optionally present) in operativecommunication with the source device 12 and the destination device 14.The video coding system 10′ of FIG. 1B, and components thereof, areotherwise similar to the video coding system 10 of FIG. 1A, andcomponents thereof.

The video encoder 20 and the video decoder 30 may operate according to avideo compression standard, such as HEVC, and may conform to a HEVC TestModel (HM). Alternatively, the video encoder 20 and the video decoder 30may operate according to other proprietary or industry standards, suchas the ITU-T H.264 standard, alternatively referred to as MPEG-4, Part10, AVC, or extensions of such standards. The techniques of thisdisclosure, however, are not limited to any particular coding standard.Other examples of video compression standards include MPEG-2 and ITU-TH.263.

Although not shown in the examples of FIGS. 1A and 1B, the video encoder20 and the video decoder 30 may each be integrated with an audio encoderand decoder, and may include appropriate MUX-DEMUX units, or otherhardware and software, to handle encoding of both audio and video in acommon data stream or separate data streams. If applicable, in someexamples, MUX-DEMUX units may conform to the ITU H.223 multiplexerprotocol, or other protocols such as the user datagram protocol (UDP).

The video encoder 20 and the video decoder 30 each may be implemented asany of a variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of the video encoder 20 and the video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder in a respective device.

Video Coding Process

As mentioned briefly above, the video encoder 20 encodes video data. Thevideo data may comprise one or more pictures. Each of the pictures is astill image forming part of a video. In some instances, a picture may bereferred to as a video “frame.” When the video encoder 20 encodes thevideo data, the video encoder 20 may generate a bitstream. The bitstreammay include a sequence of bits that form a coded representation of thevideo data. The bitstream may include coded pictures and associateddata. A coded picture is a coded representation of a picture.

To generate the bitstream, the video encoder 20 may perform encodingoperations on each picture in the video data. When the video encoder 20performs encoding operations on the pictures, the video encoder 20 maygenerate a series of coded pictures and associated data. The associateddata may include video parameter sets (VPS), sequence parameter sets(SPSs), picture parameter sets (PPSs), adaptation parameter sets (APSs),and other syntax structures. An SPS may contain parameters applicable tozero or more sequences of pictures. A PPS may contain parametersapplicable to zero or more pictures. An APS may contain parametersapplicable to zero or more pictures. Parameters in an APS may beparameters that are more likely to change than parameters in a PPS.

To generate a coded picture, the video encoder 20 may partition apicture into equally-sized video blocks. A video block may be atwo-dimensional array of samples. Each of the video blocks is associatedwith a treeblock. In some instances, a treeblock may be referred to as alargest coding unit (LCU). The treeblocks of HEVC may be broadlyanalogous to the macroblocks of previous standards, such as H.264/AVC.However, a treeblock is not necessarily limited to a particular size andmay include one or more coding units (CUs). The video encoder 20 may usequadtree partitioning to partition the video blocks of treeblocks intovideo blocks associated with CUs, hence the name “treeblocks.”

In some examples, the video encoder 20 may partition a picture into aplurality of slices. Each of the slices may include an integer number ofCUs. In some instances, a slice comprises an integer number oftreeblocks. In other instances, a boundary of a slice may be within atreeblock.

As part of performing an encoding operation on a picture, the videoencoder 20 may perform encoding operations on each slice of the picture.When the video encoder 20 performs an encoding operation on a slice, thevideo encoder 20 may generate encoded data associated with the slice.The encoded data associated with the slice may be referred to as a“coded slice.”

To generate a coded slice, the video encoder 20 may perform encodingoperations on each treeblock in a slice. When the video encoder 20performs an encoding operation on a treeblock, the video encoder 20 maygenerate a coded treeblock. The coded treeblock may comprise datarepresenting an encoded version of the treeblock.

When the video encoder 20 generates a coded slice, the video encoder 20may perform encoding operations on (e.g., encode) the treeblocks in theslice according to a raster scan order. For example, the video encoder20 may encode the treeblocks of the slice in an order that proceeds fromleft to right across a topmost row of treeblocks in the slice, then fromleft to right across a next lower row of treeblocks, and so on until thevideo encoder 20 has encoded each of the treeblocks in the slice.

As a result of encoding the treeblocks according to the raster scanorder, the treeblocks above and to the left of a given treeblock mayhave been encoded, but treeblocks below and to the right of the giventreeblock have not yet been encoded. Consequently, the video encoder 20may be able to access information generated by encoding treeblocks aboveand to the left of the given treeblock when encoding the giventreeblock. However, the video encoder 20 may be unable to accessinformation generated by encoding treeblocks below and to the right ofthe given treeblock when encoding the given treeblock.

To generate a coded treeblock, the video encoder 20 may recursivelyperform quadtree partitioning on the video block of the treeblock todivide the video block into progressively smaller video blocks. Each ofthe smaller video blocks may be associated with a different CU. Forexample, the video encoder 20 may partition the video block of atreeblock into four equally-sized sub-blocks, partition one or more ofthe sub-blocks into four equally-sized sub-sub-blocks, and so on. Apartitioned CU may be a CU whose video block is partitioned into videoblocks associated with other CUs. A non-partitioned CU may be a CU whosevideo block is not partitioned into video blocks associated with otherCUs.

One or more syntax elements in the bitstream may indicate a maximumnumber of times the video encoder 20 may partition the video block of atreeblock. A video block of a CU may be square in shape. The size of thevideo block of a CU (e.g., the size of the CU) may range from 8×8 pixelsup to the size of a video block of a treeblock (e.g., the size of thetreeblock) with a maximum of 64×64 pixels or greater.

The video encoder 20 may perform encoding operations on (e.g., encode)each CU of a treeblock according to a z-scan order. In other words, thevideo encoder 20 may encode a top-left CU, a top-right CU, a bottom-leftCU, and then a bottom-right CU, in that order. When the video encoder 20performs an encoding operation on a partitioned CU, the video encoder 20may encode CUs associated with sub-blocks of the video block of thepartitioned CU according to the z-scan order. In other words, the videoencoder 20 may encode a CU associated with a top-left sub-block, a CUassociated with a top-right sub-block, a CU associated with abottom-left sub-block, and then a CU associated with a bottom-rightsub-block, in that order.

As a result of encoding the CUs of a treeblock according to a z-scanorder, the CUs above, above-and-to-the-left, above-and-to-the-right,left, and below-and-to-the left of a given CU may have been encoded. CUsbelow and to the right of the given CU have not yet been encoded.Consequently, the video encoder 20 may be able to access informationgenerated by encoding some CUs that neighbor the given CU when encodingthe given CU. However, the video encoder 20 may be unable to accessinformation generated by encoding other CUs that neighbor the given CUwhen encoding the given CU.

When the video encoder 20 encodes a non-partitioned CU, the videoencoder 20 may generate one or more prediction units (PUs) for the CU.Each of the PUs of the CU may be associated with a different video blockwithin the video block of the CU. The video encoder 20 may generate apredicted video block for each PU of the CU. The predicted video blockof a PU may be a block of samples. The video encoder 20 may use intraprediction or inter prediction to generate the predicted video block fora PU.

When the video encoder 20 uses intra prediction to generate thepredicted video block of a PU, the video encoder 20 may generate thepredicted video block of the PU based on decoded samples of the pictureassociated with the PU. If the video encoder 20 uses intra prediction togenerate predicted video blocks of the PUs of a CU, the CU is anintra-predicted CU. When the video encoder 20 uses inter prediction togenerate the predicted video block of the PU, the video encoder 20 maygenerate the predicted video block of the PU based on decoded samples ofone or more pictures other than the picture associated with the PU. Ifthe video encoder 20 uses inter prediction to generate predicted videoblocks of the PUs of a CU, the CU is an inter-predicted CU.

Furthermore, when the video encoder 20 uses inter prediction to generatea predicted video block for a PU, the video encoder 20 may generatemotion information for the PU. The motion information for a PU mayindicate one or more reference blocks of the PU. Each reference block ofthe PU may be a video block within a reference picture. The referencepicture may be a picture other than the picture associated with the PU.In some instances, a reference block of a PU may also be referred to asthe “reference sample” of the PU. The video encoder 20 may generate thepredicted video block for the PU based on the reference blocks of thePU.

After the video encoder 20 generates predicted video blocks for one ormore PUs of a CU, the video encoder 20 may generate residual data forthe CU based on the predicted video blocks for the PUs of the CU. Theresidual data for the CU may indicate differences between samples in thepredicted video blocks for the PUs of the CU and the original videoblock of the CU.

Furthermore, as part of performing an encoding operation on anon-partitioned CU, the video encoder 20 may perform recursive quadtreepartitioning on the residual data of the CU to partition the residualdata of the CU into one or more blocks of residual data (e.g., residualvideo blocks) associated with transform units (TUs) of the CU. Each TUof a CU may be associated with a different residual video block.

The video encoder 20 may apply one or more transforms to residual videoblocks associated with the TUs to generate transform coefficient blocks(e.g., blocks of transform coefficients) associated with the TUs.Conceptually, a transform coefficient block may be a two-dimensional(2D) matrix of transform coefficients.

After generating a transform coefficient block, the video encoder 20 mayperform a quantization process on the transform coefficient block.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the transform coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the transform coefficients. For example, an n-bit transformcoefficient may be rounded down to an m-bit transform coefficient duringquantization, where n is greater than m.

The video encoder 20 may associate each CU with a quantization parameter(QP) value. The QP value associated with a CU may determine how thevideo encoder 20 quantizes transform coefficient blocks associated withthe CU. The video encoder 20 may adjust the degree of quantizationapplied to the transform coefficient blocks associated with a CU byadjusting the QP value associated with the CU.

After the video encoder 20 quantizes a transform coefficient block, thevideo encoder 20 may generate sets of syntax elements that represent thetransform coefficients in the quantized transform coefficient block. Thevideo encoder 20 may apply entropy encoding operations, such as ContextAdaptive Binary Arithmetic Coding (CABAC) operations, to some of thesesyntax elements. Other entropy coding techniques such ascontext-adaptive variable-length coding (CAVLC), probability intervalpartitioning entropy (PIPE) coding, or other binary arithmetic codingcould also be used.

The bitstream generated by the video encoder 20 may include a series ofNetwork Abstraction Layer (NAL) units. Each of the NAL units may be asyntax structure containing an indication of a type of data in the NALunit and bytes containing the data. For example, a NAL unit may containdata representing a video parameter set, a sequence parameter set, apicture parameter set, a coded slice, SEI, an access unit delimiter,filler data, or another type of data. The data in a NAL unit may includevarious syntax structures.

The video decoder 30 may receive the bitstream generated by the videoencoder 20. The bitstream may include a coded representation of thevideo data encoded by the video encoder 20. When the video decoder 30receives the bitstream, the video decoder 30 may perform a parsingoperation on the bitstream. When the video decoder 30 performs theparsing operation, the video decoder 30 may extract syntax elements fromthe bitstream. The video decoder 30 may reconstruct the pictures of thevideo data based on the syntax elements extracted from the bitstream.The process to reconstruct the video data based on the syntax elementsmay be generally reciprocal to the process performed by the videoencoder 20 to generate the syntax elements.

After the video decoder 30 extracts the syntax elements associated witha CU, the video decoder 30 may generate predicted video blocks for thePUs of the CU based on the syntax elements. In addition, the videodecoder 30 may inverse quantize transform coefficient blocks associatedwith TUs of the CU. The video decoder 30 may perform inverse transformson the transform coefficient blocks to reconstruct residual video blocksassociated with the TUs of the CU. After generating the predicted videoblocks and reconstructing the residual video blocks, the video decoder30 may reconstruct the video block of the CU based on the predictedvideo blocks and the residual video blocks. In this way, the videodecoder 30 may reconstruct the video blocks of CUs based on the syntaxelements in the bitstream.

Video Encoder

FIG. 2 is a block diagram illustrating an example of the video encoder20 that may implement techniques in accordance with aspects described inthis disclosure. The video encoder 20 may be configured to process asingle layer of a video frame, such as for HEVC. Further, the videoencoder 20 may be configured to perform any or all of the techniques ofthis disclosure. In some examples, the techniques described in thisdisclosure may be shared among the various components of the videoencoder 20. In some examples, additionally or alternatively, a processor(not shown) may be configured to perform any or all of the techniquesdescribed in this disclosure.

For purposes of explanation, this disclosure describes the video encoder20 in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 2 is for a single layer codec. However, incertain embodiments, some or all of the video encoder 20 may beduplicated for processing of a multi-layer codec.

The video encoder 20 may perform intra- and inter-coding of video blockswithin video slices. Intra coding relies on spatial prediction to reduceor remove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased coding modes. Inter-modes, such as uni-directional prediction (Pmode) or bi-directional prediction (B mode), may refer to any of severaltemporal-based coding modes.

In the example of FIG. 2, the video encoder 20 includes a plurality offunctional components. The functional components of the video encoder 20include a prediction processing unit 100, a residual generation unit102, a transform processing unit 104, a quantization unit 106, aninverse quantization unit 108, an inverse transform unit 110, areconstruction unit 112, a filter unit 113, a decoded picture buffer114, and an entropy encoding unit 116. Prediction processing unit 100includes an inter prediction unit 121, a motion estimation unit 122, amotion compensation unit 124, an intra prediction unit 126, and aninter-layer prediction unit 128. In other examples, the video encoder 20may include more, fewer, or different functional components.Furthermore, motion estimation unit 122 and motion compensation unit 124may be highly integrated, but are represented in the example of FIG. 2separately for purposes of explanation.

The video encoder 20 may receive video data. The video encoder 20 mayreceive the video data from various sources. For example, the videoencoder 20 may receive the video data from video source 18 (e.g., shownin FIG. 1A or 1B) or another source. The video data may represent aseries of pictures. To encode the video data, the video encoder 20 mayperform an encoding operation on each of the pictures. As part ofperforming the encoding operation on a picture, the video encoder 20 mayperform encoding operations on each slice of the picture. As part ofperforming an encoding operation on a slice, the video encoder 20 mayperform encoding operations on treeblocks in the slice.

As part of performing an encoding operation on a treeblock, predictionprocessing unit 100 may perform quadtree partitioning on the video blockof the treeblock to divide the video block into progressively smallervideo blocks. Each of the smaller video blocks may be associated with adifferent CU. For example, prediction processing unit 100 may partitiona video block of a treeblock into four equally sized sub-blocks,partition one or more of the sub-blocks into four equally-sizedsub-sub-blocks, and so on.

The sizes of the video blocks associated with CUs may range from 8×8samples up to the size of the treeblock with a maximum of 64×64 samplesor greater. In this disclosure, “N×N” and “N by N” may be usedinterchangeably to refer to the sample dimensions of a video block interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 video block has sixteen samples in avertical direction (y=16) and sixteen samples in a horizontal direction(x=16). Likewise, an N×N block generally has N samples in a verticaldirection and N samples in a horizontal direction, where N represents anonnegative integer value.

Furthermore, as part of performing the encoding operation on atreeblock, prediction processing unit 100 may generate a hierarchicalquadtree data structure for the treeblock. For example, a treeblock maycorrespond to a root node of the quadtree data structure. If predictionprocessing unit 100 partitions the video block of the treeblock intofour sub-blocks, the root node has four child nodes in the quadtree datastructure. Each of the child nodes corresponds to a CU associated withone of the sub-blocks. If prediction processing unit 100 partitions oneof the sub-blocks into four sub-sub-blocks, the node corresponding tothe CU associated with the sub-block may have four child nodes, each ofwhich corresponds to a CU associated with one of the sub-sub-blocks.

Each node of the quadtree data structure may contain syntax data (e.g.,syntax elements) for the corresponding treeblock or CU. For example, anode in the quadtree may include a split flag that indicates whether thevideo block of the CU corresponding to the node is partitioned (e.g.,split) into four sub-blocks. Syntax elements for a CU may be definedrecursively, and may depend on whether the video block of the CU issplit into sub-blocks. A CU whose video block is not partitioned maycorrespond to a leaf node in the quadtree data structure. A codedtreeblock may include data based on the quadtree data structure for acorresponding treeblock.

The video encoder 20 may perform encoding operations on eachnon-partitioned CU of a treeblock. When the video encoder 20 performs anencoding operation on a non-partitioned CU, the video encoder 20generates data representing an encoded representation of thenon-partitioned CU.

As part of performing an encoding operation on a CU, predictionprocessing unit 100 may partition the video block of the CU among one ormore PUs of the CU. The video encoder 20 and the video decoder 30 maysupport various PU sizes. Assuming that the size of a particular CU is2N×2N, the video encoder 20 and the video decoder 30 may support PUsizes of 2N×2N or N×N, and inter-prediction in symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, 2N×nU, nL×2N, nR×2N, or similar. The videoencoder 20 and the video decoder 30 may also support asymmetricpartitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N. In someexamples, prediction processing unit 100 may perform geometricpartitioning to partition the video block of a CU among PUs of the CIJalong a boundary that does not meet the sides of the video block of theCU at right angles.

Inter prediction unit 121 may perform inter prediction on each PU of theCU. Inter prediction may provide temporal compression. To perform interprediction on a PU, motion estimation unit 122 may generate motioninformation for the PU. Motion compensation unit 124 may generate apredicted video block for the PU based the motion information anddecoded samples of pictures other than the picture associated with theCU (e.g., reference pictures). In this disclosure, a predicted videoblock generated by motion compensation unit 124 may be referred to as aninter-predicted video block.

Slices may be I slices, P slices, or B slices. Motion estimation unit122 and motion compensation unit 124 may perform different operationsfor a PU of a CU depending on whether the PU is in an I slice, a Pslice, or a B slice. In an I slice, all PUs are intra predicted. Hence,if the PU is in an I slice, motion estimation unit 122 and motioncompensation unit 124 do not perform inter prediction on the PU.

If the PU is in a P slice, the picture containing the PU is associatedwith a list of reference pictures referred to as “list 0.” Each of thereference pictures in list 0 contains samples that may be used for interprediction of other pictures. When motion estimation unit 122 performsthe motion estimation operation with regard to a PU in a P slice, motionestimation unit 122 may search the reference pictures in list 0 for areference block for the PU. The reference block of the PU may be a setof samples, e.g., a block of samples that most closely corresponds tothe samples in the video block of the PU. Motion estimation unit 122 mayuse a variety of metrics to determine how closely a set of samples in areference picture corresponds to the samples in the video block of a PU.For example, motion estimation unit 122 may determine how closely a setof samples in a reference picture corresponds to the samples in thevideo block of a PU by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics.

After identifying a reference block of a PU in a P slice, motionestimation unit 122 may generate a reference index that indicates thereference picture in list 0 containing the reference block and a motionvector that indicates a spatial displacement between the PU and thereference block. In various examples, motion estimation unit 122 maygenerate motion vectors to varying degrees of precision. For example,motion estimation unit 122 may generate motion vectors at one-quartersample precision, one-eighth sample precision, or other fractionalsample precision. In the case of fractional sample precision, referenceblock values may be interpolated from integer-position sample values inthe reference picture. Motion estimation unit 122 may output thereference index and the motion vector as the motion information of thePU. Motion compensation unit 124 may generate a predicted video block ofthe PU based on the reference block identified by the motion informationof the PU.

If the PU is in a B slice, the picture containing the PU may beassociated with two lists of reference pictures, referred to as “list 0”and “list 1.” In some examples, a picture containing a B slice may beassociated with a list combination that is a combination of list 0 andlist 1.

Furthermore, if the PU is in a B slice, motion estimation unit 122 mayperform uni-directional prediction or bi-directional prediction for thePU. When motion estimation unit 122 performs uni-directional predictionfor the PU, motion estimation unit 122 may search the reference picturesof list 0 or list 1 for a reference block for the PU. Motion estimationunit 122 may then generate a reference index that indicates thereference picture in list 0 or list 1 that contains the reference blockand a motion vector that indicates a spatial displacement between the PUand the reference block. Motion estimation unit 122 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the PU. The prediction direction indicatormay indicate whether the reference index indicates a reference picturein list 0 or list 1. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference block indicatedby the motion information of the PU.

When motion estimation unit 122 performs bi-directional prediction for aPU, motion estimation unit 122 may search the reference pictures in list0 for a reference block for the PU and may also search the referencepictures in list 1 for another reference block for the PU. Motionestimation unit 122 may then generate reference indexes that indicatethe reference pictures in list 0 and list 1 containing the referenceblocks and motion vectors that indicate spatial displacements betweenthe reference blocks and the PU. Motion estimation unit 122 may outputthe reference indexes and the motion vectors of the PU as the motioninformation of the PU. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference blocks indicatedby the motion information of the PU.

In some instances, motion estimation unit 122 does not output a full setof motion information for a PU to entropy encoding unit 116. Rather,motion estimation unit 122 may signal the motion information of a PUwith reference to the motion information of another PU. For example,motion estimation unit 122 may determine that the motion information ofthe PU is sufficiently similar to the motion information of aneighboring PU. In this example, motion estimation unit 122 mayindicate, in a syntax structure associated with the PU, a value thatindicates to the video decoder 30 that the PU has the same motioninformation as the neighboring PU. In another example, motion estimationunit 122 may identify, in a syntax structure associated with the PU, aneighboring PU and a motion vector difference (MVD). The motion vectordifference indicates a difference between the motion vector of the PUand the motion vector of the indicated neighboring PU. The video decoder30 may use the motion vector of the indicated neighboring PU and themotion vector difference to determine the motion vector of the PU. Byreferring to the motion information of a first PU when signaling themotion information of a second PU, the video encoder 20 may be able tosignal the motion information of the second PU using fewer bits.

As part of performing an encoding operation on a CU, intra predictionunit 126 may perform intra prediction on PUs of the CU. Intra predictionmay provide spatial compression. When intra prediction unit 126 performsintra prediction on a PU, intra prediction unit 126 may generateprediction data for the PU based on decoded samples of other PUs in thesame picture. The prediction data for the PU may include a predictedvideo block and various syntax elements. Intra prediction unit 126 mayperform intra prediction on PUs in I slices, P slices, and B slices.

To perform intra prediction on a PU, intra prediction unit 126 may usemultiple intra prediction modes to generate multiple sets of predictiondata for the PU. When intra prediction unit 126 uses an intra predictionmode to generate a set of prediction data for the PU, intra predictionunit 126 may extend samples from video blocks of neighboring PUs acrossthe video block of the PU in a direction and/or gradient associated withthe intra prediction mode. The neighboring PUs may be above, above andto the right, above and to the left, or to the left of the PU, assuminga left-to-right, top-to-bottom encoding order for PUs, CUs, andtreeblocks. Intra prediction unit 126 may use various numbers of intraprediction modes, e.g., 33 directional intra prediction modes, dependingon the size of the PU.

Prediction processing unit 100 may select the prediction data for a PUfrom among the prediction data generated by motion compensation unit 124for the PU or the prediction data generated by intra prediction unit 126for the PU. In some examples, prediction processing unit 100 selects theprediction data for the PU based on rate/distortion metrics of the setsof prediction data.

If prediction processing unit 100 selects prediction data generated byintra prediction unit 126, prediction processing unit 100 may signal theintra prediction mode that was used to generate the prediction data forthe PUs, e.g., the selected intra prediction mode. Prediction processingunit 100 may signal the selected intra prediction mode in various ways.For example, it may be probable that the selected intra prediction modeis the same as the intra prediction mode of a neighboring PU. In otherwords, the intra prediction mode of the neighboring PU may be the mostprobable mode for the current PU. Thus, prediction processing unit 100may generate a syntax element to indicate that the selected intraprediction mode is the same as the intra prediction mode of theneighboring PU.

As discussed above, the video encoder 20 may include inter-layerprediction unit 128. Inter-layer prediction unit 128 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SHVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 128 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer.

After prediction processing unit 100 selects the prediction data for PUsof a CU, residual generation unit 102 may generate residual data for theCU by subtracting (e.g., indicated by the minus sign) the predictedvideo blocks of the PUs of the CU from the video block of the CU. Theresidual data of a CU may include 2D residual video blocks thatcorrespond to different sample components of the samples in the videoblock of the CU. For example, the residual data may include a residualvideo block that corresponds to differences between luminance componentsof samples in the predicted video blocks of the PUs of the CU andluminance components of samples in the original video block of the CU.In addition, the residual data of the CU may include residual videoblocks that correspond to the differences between chrominance componentsof samples in the predicted video blocks of the PUs of the CU and thechrominance components of the samples in the original video block of theCU.

Prediction processing unit 100 may perform quadtree partitioning topartition the residual video blocks of a CU into sub-blocks. Eachundivided residual video block may be associated with a different TU ofthe CU. The sizes and positions of the residual video blocks associatedwith TUs of a CU may or may not be based on the sizes and positions ofvideo blocks associated with the PUs of the CU. A quadtree structureknown as a “residual quad tree” (RQT) may include nodes associated witheach of the residual video blocks. The TUs of a CU may correspond toleaf nodes of the RQT.

Transform processing unit 104 may generate one or more transformcoefficient blocks for each TU of a CU by applying one or moretransforms to a residual video block associated with the TU. Each of thetransform coefficient blocks may be a 2D matrix of transformcoefficients. Transform processing unit 104 may apply various transformsto the residual video block associated with a TU. For example, transformprocessing unit 104 may apply a discrete cosine transform (DCT), adirectional transform, or a conceptually similar transform to theresidual video block associated with a TU.

After transform processing unit 104 generates a transform coefficientblock associated with a TU, quantization unit 106 may quantize thetransform coefficients in the transform coefficient block. Quantizationunit 106 may quantize a transform coefficient block associated with a TUof a CU based on a QP value associated with the CU.

The video encoder 20 may associate a QP value with a CU in various ways.For example, the video encoder 20 may perform a rate-distortion analysison a treeblock associated with the CU. In the rate-distortion analysis,the video encoder 20 may generate multiple coded representations of thetreeblock by performing an encoding operation multiple times on thetreeblock. The video encoder 20 may associate different QP values withthe CU when the video encoder 20 generates different encodedrepresentations of the treeblock. The video encoder 20 may signal that agiven QP value is associated with the CU when the given QP value isassociated with the CU in a coded representation of the treeblock thathas a lowest bitrate and distortion metric.

Inverse quantization unit 108 and inverse transform unit 110 may applyinverse quantization and inverse transforms to the transform coefficientblock, respectively, to reconstruct a residual video block from thetransform coefficient block. Reconstruction unit 112 may add thereconstructed residual video block to corresponding samples from one ormore predicted video blocks generated by prediction processing unit 100to produce a reconstructed video block associated with a TU. Byreconstructing video blocks for each TU of a CU in this way, the videoencoder 20 may reconstruct the video block of the CU.

After reconstruction unit 112 reconstructs the video block of a CU,filter unit 113 may perform a deblocking operation to reduce blockingartifacts in the video block associated with the CU. After performingthe one or more deblocking operations, filter unit 113 may store thereconstructed video block of the CU in decoded picture buffer 114.Motion estimation unit 122 and motion compensation unit 124 may use areference picture that contains the reconstructed video block to performinter prediction on PUs of subsequent pictures. In addition, intraprediction unit 126 may use reconstructed video blocks in decodedpicture buffer 114 to perform intra prediction on other PUs in the samepicture as the CU.

Entropy encoding unit 116 may receive data from other functionalcomponents of the video encoder 20. For example, entropy encoding unit116 may receive transform coefficient blocks from quantization unit 106and may receive syntax elements from prediction processing unit 100.When entropy encoding unit 116 receives the data, entropy encoding unit116 may perform one or more entropy encoding operations to generateentropy encoded data. For example, the video encoder 20 may perform aCAVLC operation, a CABAC operation, a variable-to-variable (V2V) lengthcoding operation, a syntax-based context-adaptive binary arithmeticcoding (SBAC) operation, a Probability Interval Partitioning Entropy(PIPE) coding operation, or another type of entropy encoding operationon the data. Entropy encoding unit 116 may output a bitstream thatincludes the entropy encoded data.

As part of performing an entropy encoding operation on data, entropyencoding unit 116 may select a context model. If entropy encoding unit116 is performing a CABAC operation, the context model may indicateestimates of probabilities of particular bins having particular values.In the context of CABAC, the term “bin” is used to refer to a bit of abinarized version of a syntax element.

Video Decoder

FIG. 3 is a block diagram illustrating an example of the video decoder30 that may implement techniques in accordance with aspects described inthis disclosure. The video decoder 30 may be configured to process asingle layer of a video frame, such as for HEVC. Further, the videodecoder 30 may be configured to perform any or all of the techniques ofthis disclosure. In some examples, the techniques described in thisdisclosure may be shared among the various components of the videodecoder 30. In some examples, additionally or alternatively, a processor(not shown) may be configured to perform any or all of the techniquesdescribed in this disclosure.

For purposes of explanation, this disclosure describes the video decoder30 in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 3 is for a single layer codec. However, incertain implementations, some or all of the video decoder 30 may beduplicated for processing of a multi-layer codec.

In the example of FIG. 3, the video decoder 30 includes a plurality offunctional components. The functional components of the video decoder 30include an entropy decoding unit 150, a prediction processing unit 152,an inverse quantization unit 154, an inverse transform unit 156, areconstruction unit 158, a filter unit 159, and a decoded picture buffer160. Prediction processing unit 152 includes a motion compensation unit162, an intra prediction unit 164, and an inter-layer prediction unit166. In some examples, the video decoder 30 may perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 20 of FIG. 2. In other examples, the video decoder 30 mayinclude more, fewer, or different functional components.

The video decoder 30 may receive a bitstream that comprises encodedvideo data. The bitstream may include a plurality of syntax elements.When the video decoder 30 receives the bitstream, entropy decoding unit150 may perform a parsing operation on the bitstream. As a result ofperforming the parsing operation on the bitstream, entropy decoding unit150 may extract syntax elements from the bitstream. As part ofperforming the parsing operation, entropy decoding unit 150 may entropydecode entropy encoded syntax elements in the bitstream. Predictionprocessing unit 152, inverse quantization unit 154, inverse transformunit 156, reconstruction unit 158, and filter unit 159 may perform areconstruction operation that generates decoded video data based on thesyntax elements extracted from the bitstream.

As discussed above, the bitstream may comprise a series of NAL units.The NAL units of the bitstream may include video parameter set NALunits, sequence parameter set NAL units, picture parameter set NALunits, SEI NAL units, and so on. As part of performing the parsingoperation on the bitstream, entropy decoding unit 150 may performparsing operations that extract and entropy decode sequence parametersets from sequence parameter set NAL units, picture parameter sets frompicture parameter set NAL units, SEI data from SEI NAL units, and so on.

In addition, the NAL units of the bitstream may include coded slice NALunits. As part of performing the parsing operation on the bitstream,entropy decoding unit 150 may perform parsing operations that extractand entropy decode coded slices from the coded slice NAL units. Each ofthe coded slices may include a slice header and slice data. The sliceheader may contain syntax elements pertaining to a slice. The syntaxelements in the slice header may include a syntax element thatidentifies a picture parameter set associated with a picture thatcontains the slice. Entropy decoding unit 150 may perform entropydecoding operations, such as CABAC decoding operations, on syntaxelements in the coded slice header to recover the slice header.

As part of extracting the slice data from coded slice NAL, units,entropy decoding unit 150 may perform parsing operations that extractsyntax elements from coded CUs in the slice data. The extracted syntaxelements may include syntax elements associated with transformcoefficient blocks. Entropy decoding unit 150 may then perform CABACdecoding operations on some of the syntax elements.

After entropy decoding unit 150 performs a parsing operation on anon-partitioned CU, the video decoder 30 may perform a reconstructionoperation on the non-partitioned CU. To perform the reconstructionoperation on a non-partitioned CU, the video decoder 30 may perform areconstruction operation on each TU of the CU. By performing thereconstruction operation for each TU of the CU, the video decoder 30 mayreconstruct a residual video block associated with the CU.

As part of performing a reconstruction operation on a TU, inversequantization unit 154 may inverse quantize, e.g., de-quantize, atransform coefficient block associated with the TU. Inverse quantizationunit 154 may inverse quantize the transform coefficient block in amanner similar to the inverse quantization processes proposed for HEVCor defined by the H.264 decoding standard. Inverse quantization unit 154may use a quantization parameter QP calculated by the video encoder 20for a CU of the transform coefficient block to determine a degree ofquantization and, likewise, a degree of inverse quantization for inversequantization unit 154 to apply.

After inverse quantization unit 154 inverse quantizes a transformcoefficient block, inverse transform unit 156 may generate a residualvideo block for the TU associated with the transform coefficient block.Inverse transform unit 156 may apply an inverse transform to thetransform coefficient block in order to generate the residual videoblock for the TU. For example, inverse transform unit 156 may apply aninverse DCT, an inverse integer transform, an inverse Karhunen-Loevetransform (KLT), an inverse rotational transform, an inverse directionaltransform, or another inverse transform to the transform coefficientblock. In some examples, inverse transform unit 156 may determine aninverse transform to apply to the transform coefficient block based onsignaling from the video encoder 20. In such examples, inverse transformunit 156 may determine the inverse transform based on a signaledtransform at the root node of a quadtree for a treeblock associated withthe transform coefficient block. In other examples, inverse transformunit 156 may infer the inverse transform from one or more codingcharacteristics, such as block size, coding mode, or the like. In someexamples, inverse transform unit 156 may apply a cascaded inversetransform.

In some examples, motion compensation unit 162 may refine the predictedvideo block of a PU by performing interpolation based on interpolationfilters. Identifiers for interpolation filters to be used for motioncompensation with sub-sample precision may be included in the syntaxelements. Motion compensation unit 162 may use the same interpolationfilters used by the video encoder 20 during generation of the predictedvideo block of the PU to calculate interpolated values for sub-integersamples of a reference block. Motion compensation unit 162 may determinethe interpolation filters used by the video encoder 20 according toreceived syntax information and use the interpolation filters to producethe predicted video block.

If a PU is encoded using intra prediction, intra prediction unit 164 mayperform intra prediction to generate a predicted video block for the PU.For example, intra prediction unit 164 may determine an intra predictionmode for the PU based on syntax elements in the bitstream. The bitstreammay include syntax elements that intra prediction unit 164 may use todetermine the intra prediction mode of the PU.

In some instances, the syntax elements may indicate that intraprediction unit 164 is to use the intra prediction mode of another PU todetermine the intra prediction mode of the current PU. For example, itmay be probable that the intra prediction mode of the current PU is thesame as the intra prediction mode of a neighboring PU. In other words,the intra prediction mode of the neighboring PU may be the most probablemode for the current PU. Hence, in this example, the bitstream mayinclude a small syntax element that indicates that the intra predictionmode of the PU is the same as the intra prediction mode of theneighboring PU. Intra prediction unit 164 may then use the intraprediction mode to generate prediction data (e.g., predicted samples)for the PU based on the video blocks of spatially neighboring PUs.

As discussed above, the video decoder 30 may also include inter-layerprediction unit 166. Inter-layer prediction unit 166 is configured topredict a current block (e.g., a current block in the enhancement layer)using one or more different layers that are available in SHVC (e.g., abase or reference layer). Such prediction may be referred to asinter-layer prediction. Inter-layer prediction unit 166 utilizesprediction methods to reduce inter-layer redundancy, thereby improvingcoding efficiency and reducing computational resource requirements. Someexamples of inter-layer prediction include inter-layer intra prediction,inter-layer motion prediction, and inter-layer residual prediction.Inter-layer intra prediction uses the reconstruction of co-locatedblocks in the base layer to predict the current block in the enhancementlayer. Inter-layer motion prediction uses motion information of the baselayer to predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

Reconstruction unit 158 may use the residual video blocks associatedwith TUs of a CU and the predicted video blocks of the PUs of the CU,e.g., either intra prediction data or inter-prediction data, asapplicable, to reconstruct the video block of the CU. Thus, the videodecoder 30 may generate a predicted video block and a residual videoblock based on syntax elements in the bitstream and may generate a videoblock based on the predicted video block and the residual video block.

After reconstruction unit 158 reconstructs the video block of the CU,tilter unit 159 may perform a deblocking operation to reduce blockingartifacts associated with the CU. After filter unit 159 performs adeblocking operation to reduce blocking artifacts associated with theCU, the video decoder 30 may store the video block of the CU in decodedpicture buffer 160. Decoded picture buffer 160 may provide referencepictures for subsequent motion compensation, intra prediction, andpresentation on a display device, such as display device 32 of FIG. 1Aor 1B. For instance, the video decoder 30 may perform, based on thevideo blocks in decoded picture buffer 160, intra prediction or interprediction operations on PUs of other CUs.

Palette Coding Mode

In contrast to conventional intra and inter prediction that mainlyremoves redundancy between different coding units, palette codingtargets the redundancy of repetitive pixel values/patterns within thecoding unit. In the palette coding mode, a lookup table called a palettethat maps pixel values into table indices (also called palette indices)is signaled first. In some implementations, the palette has a specifiedmaximum size (e.g., 32 pixel values). The palette includes entriesnumbered by the table indices representing color component (e.g., RGB,YUV, etc.) values or intensities that can be used as predictors forblock samples or as final reconstructed block samples. In someimplementations, samples in a palette block are coded using threerun-modes, i.e. ‘copy-left mode’ (or run mode), ‘copy-above mode’, and‘escape mode’ (or pixel mode).

For a position in the palette block that is coded in copy-left mode, apalette index is first signaled followed by “run_length” (or“palette_run”) (e.g., M). No additional information needs to be signaledfor the current position and the following M positions in the paletteblock because the current position and the following M positions in thepalette block have the same palette index that is signaled for thecurrent position. The palette index (e.g., i) is shared by all threecolor components, which means that the reconstructed pixel values are(Y, U, V)=(palette_(Y)[i], palette_(U)[i], palette_(V)[i]) (assuming thecolor space is YUV).

For a position in the palette block that is coded in copy-above mode, avalue “run_length” (or “copy_run”) (e.g., N) is signaled to indicatethat for the following N positions (N+1 positions in total, includingthe current one) in the palette block, the palette index is equal to thepalette index of the position that is directly above in the paletteblock.

For a position in the palette block that is coded in escape mode (orpixel mode), a pixel value corresponding to the current position in thepalette block is signaled. Escape mode may be signaled using an escapeflag (e.g., a flag value of 1 indicates that the current position iscoded in escape mode) or a palette index (e.g., an index value that doesnot correspond to any of the palette entries or an index value that isgreater than or equal to the palette size).

Palette Bitstream

In existing implementations, a palette bitstream (e.g., a bitstream thatincludes coding units coded in palette coding mode) is organized asfollows:

TABLE 1 Palette mode bitstream palette_entries palette_index_map

palette_entries includes one or more pixel values each mapped to a tableindex. For example, if a given coding unit includes three unique pixelvalues (e.g., red, green, and blue), the palette entries may includethree entries, (0, red), (1, green), and (2, blue), palette_index_mapincludes one or more palette blocks coded using the palette entries,where palette table indices (e.g., 0, 1, and 2 in the example above) areused to indicate the pixel values in the palette block.

FIG. 4 illustrates an example configuration of input CU 410, index block420, escape pixel 430, and palette 440. As shown in FIG. 4, the input CU410 contains three unique pixel values: white, grey, and black. Based onthe frequency of white and grey, only white and grey pixel values areincluded in the palette 440, where an index value of 0 is associatedwith the white pixel value and an index value of 1 is associated withthe grey pixel value. The black pixel value that is not included in thepalette is labeled as an escape pixel 430, which is coded independentlyof the palette. As shown in FIG. 4, the index block 420 includes anindex value for each position in the block. Two positions in the indexblock 420 are coded as in escape mode (e.g., without referring topalette indices 0 or 1). Although only a single escape pixel and onlytwo palette entries are used in the example of FIG. 4, the embodimentsof the present application are not limited as such, and any number ofescape pixels and palette entries may be used. In some embodiments, thepalette size is limited to 32 entries, and any pixel values notassociated with one of the 32 entries become escape pixels. The maximumpalette size may be set to any number. Further, the CU size is notlimited to 8 pixels by 8 pixels, and may be 16×16 or any other size.

Example Syntax of Palette Bitstream

In some implementations, in the palette index map, a block coded inpalette coding mode may take the following form in the bitstream:

TABLE 2 palette_index_map bitstream (default setting) while (not end) { run_mode_flag  if (run_mode_flag == COPY_ABOVE)   run_length  else if(run_mode_flag == COPY_LEFT) {   index   if (index == ESCAPE_INDEX)   escape_pixel_value   else    run_length }

In the example illustrated in Table 2, depending on the value ofrun_mode_flag, different syntax elements are signaled in the bitstream.If the run mode flag indicates that the current position in the paletteblock is coded in copy-above mode, the run body includes a run lengthvalue (the first instance of “run_length” above). If the run mode flagindicates that the current position in the palette block is coded in‘copy-left’ mode, the run body includes an index value (“index”)followed by a run length value (the second instance of “run_length”above), unless the index value corresponds to an escape index, in whichcase quantized escape pixel values (“escape_pixel_value”) are signaled.

In an alternative implementation, an explicit escape flag is used. Morespecifically, the palette index map may take the following form in thebitstream;

TABLE 3 palette_index_map bitstream (alternative setting) while (notend) {  escape_flag  if (escape_flag)   escape_pixel_value  else {  run_mode_flag   if (run_mode_flag == COPY_LEFT)    index   run_length}

In the example illustrated in Table 3, depending on the value of escapeflag, different syntax elements are signaled in the bitstream. If theescape flag has a value of 1, the run body includes quantized escapepixel values. If the escape flag has a value of 0, a run mode flag issignaled to differentiate ‘copy above’ and ‘copy left’ modes. If the runmode flag indicates that the current position in the palette block iscoded in ‘copy-left’ mode, the bitstream includes an index valuefollowed by a run length value. Otherwise, only a run length value issignaled in the bitstream.

FIG. 5 is a flowchart illustrating a method 500 for coding non-naturalvideo data in a bitstream in accordance with aspects of the presentdisclosure. The steps illustrated in FIG. 5 may be performed by a videoencoder (e.g., the video encoder 20), a video decoder (e.g., the videodecoder 30), or any other component. For convenience, method 500 isdescribed as performed by a video coder (also simply referred to ascoder), which may be the video encoder 20, the video decoder 30, oranother component.

The method 500 begins at block 501. At block 505, the coder processes acoding unit (CU) having a plurality of pixels based on a paletteassociated with the CU. As described above, an encoder may derive thepalette based on the content of the CU and signal the palette in thebitstream so that a decoder may process the CU using the paletteassociated with the CU. The palette may include a plurality of paletteentries that are each associated with an index value and a pixel value.The pixel value may be associated with one of the pixels in the CU. Insome embodiments, each palette entry is associated a unique pixel valuethat is found in the CU. Block 505 may comprise one or more steps and/ormethods described with reference to FIGS. 6-8. The method ends at block510.

Grouping Bypass Bins

In H.264, HEVC, and many other modern video coding standards, for asyntax element, after binarization, the 0/1 bin stream is fed into thecontext adaptive binary arithmetic coder (CABAC), in which theprobability model (named “context”) is adaptively selected and updatedto track the non-stationary probability distribution. As a special case,the probability model may not be updated to improve the entropy coder'sthroughput. Bins coded using such a simplified method without contextupdate is called bypass bins.

In the examples of Tables 2 and 3, there may be some redundancies in thebitstream. These redundancies may be removed by skipping to signalcertain syntax elements when certain conditions are satisfied. Inaddition, some syntax elements may introduce parsing dependency. Forexample, in Table 2, syntax element run_mode_flag may not need to besignaled if the current pixel is in the first line of the block, sincethe decoder may infer the run mode to be index copy mode (e.g., copyleft mode). In addition, in the example of Table 2, the decoder decodesthe index value first, and depending on the decoded index value, thedecoder decides whether the mode is index copy mode or escape mode(e.g., based on whether or not the index value represents an escapeindex value). If the decoder determines the mode to be index copy mode,the decoder parser continues to parse run length. If the decoderdetermines the mode to be escape mode, the decoder parser may continueto parse escape values and/or run length. Since parsers usually operateat a much higher speed than decoders, such dependency between decodingengine and parsing engine may affect parser's throughput (e.g., sincethe parsing engine may need to wait for the decoding engine to decodethe parsed bits). Thus, an improved method of processing blocks coded inpalette coding mode is desired. In this application, several novelmethods for organizing the palette elements in the bitstream to avoid orreduce the parsing dependency in palette mode are described.

Embodiment #1 Put Quantized Escape Pixel Values at the End of a PaletteMode Block

In some embodiments, all quantized escape pixel values are signaled atthe end of a palette mode block in the bitstream. In such embodiments,entropy coder resetting may be applied after the (index, run-length)coding. For example, after coding all of the possible (index,run-length) pairs in the block, the arithmetic coding engine'sivlCurrRange variable (e.g., a variable specifying the range of thecurrent arithmetic coding interval) is set to 256. With this method, thedecoder may read the bits from the bitstream and treat them as they arewithout needing to invoke the CABAC coder. Without this procedure ofresetting the variable to 256, while the context may not need to beupdated, the decoder may still need to invoke the CABAC coder to makebinary decisions. Therefore, the quantized escape pixel values can beparsed in parallel after parsing and/or decoding all the (index,run-length) pairs. In one embodiment, if the escape pixels are codedusing fixed length code, then the escape pixels can be parsed anddecoded in parallel after parsing the index-run block.

In another embodiment, if the escape pixels are coded using truncatedbinary code, then each color component of the escape pixel may take ‘k’or ‘k+1’ bits depending on its quantized intensity. For example, intruncated binary encoding, for a syntax element with value X, assumingthat its maximum possible value Max is known and that n=Max+1 andk−floor(log₂(n)) such that 2^(k)≦n<2^(k+1) and let u=2k+1−n, if X<u, thetruncated binary codeword is specified by the binary representation of Xwith length k. Otherwise, the truncated binary codeword is specified bythe binary representation of X+u with length k+1. In such an embodiment,the first ‘k’ bits of each color component for all the escape pixels inthe current block may be grouped together, followed by the optional(k+1)^(th) bit. With such organization, the first ‘k’ bits of each colorcomponent for all the escape pixels can be parsed and decoded inparallel. Some dependency may still exist in parsing the optional(k+1)^(th) bit.

FIG. 6 is a flowchart illustrating a method 600 for decoding non-naturalvideo data in a bitstream in accordance with aspects of the presentdisclosure. The steps illustrated in FIG. 6 may be performed by a videodecoder (e.g., the video decoder 30) or any other component. Forconvenience, method 600 is described as performed by a video coder (alsosimply referred to as coder), which may be the video decoder 30 oranother component.

The method 600 begins at block 601. At block 605, the coder parses apalette associated with the cu provided in the bitstream. The palettemay include a plurality of palette entries that are each associated withan index value and a pixel value associated with the index value. Anexample of the palette is illustrated in FIG. 4.

At block 610, the coder parses one or more run lengths associated with aCU. As described above, each run length indicates the number ofconsecutive positions, starting from and including a current position inthe CU, that are associated with a copy-left mode or a copy-above mode.

At block 615, the coder parses one or more index values associated withthe CU. As described above, each index value indicates a pixel value inthe palette that is associated with the current position in the CU. Inthe example of FIG. 4, an index value of 0 indicates that the currentposition in the CU has a white pixel value, and an index value of 1indicates that the current position in the CU has a grey pixel value.

At block 620, the coder parses one or more escape pixel valuesassociated with the CU. As described above, each escape pixel valueindicates a pixel value that is not in the palette associated with theCU. In the example of FIG. 4, the two positions in the CU having blackpixel values are coded in escape mode and the coder signals the blackpixel values in the bitstream as escape pixel values. In someembodiments, the escape pixel values are parsed from consecutivepositions in the bitstream (e.g., at the end of the portion of thebitstream associated with the CU). For example, the consecutivepositions of the escape pixel values appear in the bitstream after allthe run lengths and index values associated with the CU. In suchembodiments, after all the run lengths and the index values have beenparsed, the escape pixel values can be processed (e.g., parsed) inparallel. At block 625, the coder decodes the CU based on the parsedpalette, parsed run lengths, parsed index values, and parsed escapevalues. The method ends at block 630.

In the method 600, one or more of the blocks shown in FIG. 6 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. For example, block 610 and block 615 may beperformed together to parse each run length and index value pairassociated with the CU. In some embodiments, additional blocks may beadded to the method 600. The embodiments of the present disclosure arenot limited to or by the example shown in FIG. 6, and other variationsmay be implemented without departing from the spirit of this disclosure.

Embodiment #2 Put Index Values at the End of a Palette Mode Block

In some embodiments, all index values are signaled at the end of apalette mode block in the bitstream. In one embodiment, all quantizedescape values are signaled at the end of the palette mode block in thebitstream, following the group of all occurrences of index values. Inanother embodiment, all index values are signaled just before thequantized escape values in the bitstream.

Entropy coder resetting may be applied after the run-length coding. Forexample, after coding all of the possible run-lengths in the block, thearithmetic coding engine's ivlCurrRange variable (e.g., a variablespecifying the range of the current arithmetic coding interval) is setto 256. Therefore, the index values and/or the escape values can beparsed in parallel after parsing and/or decoding all the run-lengths inthe palette block. In one embodiment, if the index values are codedusing fixed length code, then the index values can be parsed and decodedin parallel after parsing the run-length block.

In another embodiment, if the index values are coded using truncatedbinary code, then indexes may take ‘k’ or ‘k+1’ bits depending on itsvalue. In such an embodiment, the first ‘k’ bits of each color componentfor all the index values and/or the escape pixels in the current blockmay be grouped together, followed by the optional (k+1)^(th) bit. Withsuch organization, the first ‘k’ bits of all the index values and/or theescape values in the current block can be parsed and decoded inparallel. Some dependency may still exist in parsing the optional(k+1)^(th) bit.

FIG. 7 is a flowchart illustrating a method 700 for decoding non-naturalvideo data in a bitstream in accordance with aspects of the presentdisclosure. The steps illustrated in FIG. 7 may be performed by a videodecoder (e.g., the video decoder 30) or any other component. Forconvenience, method 700 is described as performed by a video coder (alsosimply referred to as coder), which may be the video decoder 30 oranother component.

The method 700 begins at block 701. At block 705, the coder parses apalette associated with the cu provided in the bitstream. The palettemay include a plurality of palette entries that are each associated withan index value and a pixel value associated with the index value. Anexample of the palette is illustrated in FIG. 4.

At block 710, the coder parses one or more run lengths associated with aCU. As described above, each run length indicates the number ofconsecutive positions, starting from and including a current position inthe CU, that are associated with a copy-left mode or a copy-above mode.

At block 715, the coder parses one or more index values associated withthe CU. As described above, each index value indicates a pixel value inthe palette that is associated with the current position in the CU. Inthe example of FIG. 4, an index value of 0 indicates that the currentposition in the CU has a white pixel value, and an index value of 1indicates that the current position in the CU has a grey pixel value. Inthe example of FIG. 7, the index values may be parsed from consecutivepositions in the bitstream (e.g., after all of the run lengthsassociated with the CU). In such embodiments, after all the run lengthshave been parsed, the index values can be processed (e.g., parsed) inparallel. For example, the index values may be provided immediatelybefore the escape pixel values in the bitstream.

At block 720, the coder parses one or more escape pixel valuesassociated with the CU. As described above, each escape pixel valueindicates a pixel value that is not in the palette associated with theCU. In the example of FIG. 4, the two positions in the CU having blackpixel values are coded in escape mode and the coder signals the blackpixel values in the bitstream as escape pixel values. In someembodiments, the escape pixel values maybe parsed from consecutivepositions in the bitstream (e.g., at the end of the portion of thebitstream associated with the CU) For example, the consecutive positionsof the escape pixel values may appear in the bitstream after all the runlengths and index values associated with the CU. In such embodiments,after all the run lengths and the index values have been parsed, theescape pixel values can be processed (e.g., parsed) in parallel. Atblock 725, the coder decodes the CU based on the parsed palette, parsedrun lengths, parsed index values, and parsed escape values. The methodends at block 730.

In the method 700, one or more of the blocks shown in FIG. 7 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. In some embodiments, additional blocks may beadded to the method 700. The embodiments of the present disclosure arenot limited to or by the example shown in FIG. 7, and other variationsmay be implemented without departing from the spirit of this disclosure.

Embodiment #3 Use Offsets to Specify Position of Index Value and EscapePixel Value

In some embodiments, two offsets may be signaled at the beginning of apalette mode block in the bitstream, where the two offsets specify thestarting positions of the index value group and the escape pixel valuegroup discussed above, denoted, for example, by S0 and S1, respectively.In the case that the index value group is ahead of the escape pixelvalue group, only the delta value between the two starting positions maybe signaled for the second offset (e.g., offsets S0 and S1-S0 may besignaled). The two offsets can be signaled using various entropy codingmethods, e.g., Truncated-Rice, Exponential-Golomb, Truncated-Binary,Fixed Length, Unary, Truncated Unary, etc. In some embodiments, anoffset value S2 indicating the end of the palette mode block may also besignaled. Alternatively, the delta value between the second offset andS2 may be signaled (e.g., S2-S1).

Implementation of Grouping Bypass Bins

According to Embodiments #1 and #3 described above, thepalette_index_map bitstream may be modified as follows:

TABLE 4 example of modified palette_index_map bitstream while (byteposition != S0) {  run_mode_flag  if (run_mode_flag == COPY_ABOVE)  run_length  else if (run_mode_flag == COPY_LEFT) {   index   if (index!= ESCAPE_INDEX)    run_length } while (not end of block) { escape_pixel_value }

According to Embodiments #1, #2, and #3 described above, thepalette_index_map bitstream may be modified as follows:

TABLE 5 example palette_index_map bitstream while (byte position != S0){  escape_and_run_mode_flag   /*CAN BE ‘1’ ‘01’ ‘00’*/  if(escape_and_run_mode_flag != 1)   /*NOT AN ESCAPE   PIXEL*/   run_length} while (byte position != S1) {  index } while (byte position != S2) { escape_pixel_value }

Index Redundancy Check

In some embodiments, when coding the index values, a redundancy checkmay be applied. For example, if the previous neighboring position inraster scanning order (denoted as position ‘x−1’) is the end of acopy-left run mode, then the current index value cannot be the same asits previous neighboring position's index value. In other words, if theposition ‘x−1’ is valid (e.g, is within the current block or is outsidethe current block but has a deterministic value, for example, throughborder padding) and is the end of a copy-left run, then the index valuefor position ‘x’ cannot be equal to the index value at position ‘x−1’(Case 1). The reason is that if the two index values were the same, theywould have been merged into a longer copy-left run. In another example,if the previous neighboring position in raster scanning order is the endof a copy-above run mode, and/or if an additional restriction that thecurrent position's above neighbor not be an escape pixel is satisfied,then the current value cannot be the same as its top neighbor's indexvalue. In other words, if the position ‘x−1’ is valid and is the end ofa copy-above run, and/or if an additional restriction that the pixelvalue above position ‘x’ not be an escape pixel is satisfied, then theindex value for position ‘x’ cannot be equal to its above neighbor'sindex value (Case 2). The reason is that if the two index values werethe same, they would have been merged into a longer copy-above run.Thus, these examples assume that the encoder follows the ‘longestpossible run’ principle. In either of these cases, the range (e.g., Maxvalue described above) can be reduced by one and bit savings may beachieved.

However, for Case 1, the decoding of the index value at position ‘x’depends on the reconstruction of the index value at position ‘x−1’(e.g., since the decoder needs to know the index value at position ‘x−1’to determine what the index value at position ‘x’ cannot be). However,the index value for position ‘x−1’ may not be readily available by thetime the index value at position ‘x’ is being decoded. Thus, thisdependency may cause some delay in the decoding process. In order toremove this dependency, in some embodiments, the conditional check forCase 1 may be disabled. In some of such embodiments, the conditionalcheck for Case 2 may still be performed (e.g., since the index value ofa position above the current pixel is more likely to be available). Insuch embodiments, the conditional check for Case 1 is completelydisabled. Alternatively, the conditional check for Case 1 may bedisabled only for a specific case. For example, the conditional checkfor Case 1 may be disabled only when the ‘limited run’ feature isenabled, where the maximum palette index value for which the run lengthis coded (or the minimum palette index value for which the run length isnot coded) is indicated.

In Case 2, the checking of whether the pixel above position ‘x’ is anescape pixel or not can be removed if the escape pixel is admitted intocopy-left or copy-above runs. For example, the escape pixels may beassigned one or more index values that are not in the palette and havetheir own runs (e.g., just like pixel values in the palette). Similarly,the checking of whether the pixel to the left of position ‘x’ is anescape pixel or not (e.g., a step that may need to be performed beforeparsing the current index value at position x, if the givenimplementation does not allow escape pixels to be copied from the leftor from the above) can be removed if the escape pixel is admitted intocopy-left or copy-above runs

FIG. 8 is a flowchart illustrating a method 800 for coding non-naturalvideo data in a bitstream in accordance with aspects of the presentdisclosure. The steps illustrated in FIG. 8 may be performed by a videoencoder (e.g., the video encoder 20), a video decoder (e.g., the videodecoder 30), or any other component. For convenience, method 800 isdescribed as performed by a video coder (also simply referred to ascoder), which may be the video encoder 20, the video decoder 30, oranother component.

The method 800 begins at block 801. At block 805, the coder determinesthat a position to the left of a current position in the CU isassociated with the end of a copy-above run. As described above, whenone or more positions in the CU are coded in copy-above mode, a runlength indicating the number of consecutive positions, starting from andincluding the initial position in the CU, that are associated with thecopy-above mode is signaled. Based on the run length, the coder maydetermine that a given position (e.g., a position that immediatelyprecedes the current position in the CU) is the end of a copy-above run.

At block 810, the coder, in response to determining that the position tothe left of the current position is associated with the end of acopy-above run, determines the index value associated with the currentposition without determining whether the position above the currentposition is associated with an escape pixel value. As described above,typically, the coder needs to determine whether the position above thecurrent position is associated with an escape pixel value beforedetermining the index value of the current pixel (e.g., if the positionabove the current position is associated with an escape pixel, theassumption that the index value of the current position does not equalthe index value of the position above the current position may becomeinaccurate. However, in some embodiments of the present disclosure,escape pixels can be part of copy-left or copy-above runs. Thus, aseparate check on the position above the current position is not needed.The method ends at block 815.

In the method 800, one or more of the blocks shown in FIG. 8 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. In some embodiments, additional blocks may beadded to the method 800. The embodiments of the present disclosure arenot limited to or by the example shown in FIG. 8, and other variationsmay be implemented without departing from the spirit of this disclosure.

Keeping Maximum Number of Index Bins as Constant

In some implementations of palette mode coding, palette indices arecoded using truncated binary code. Assuming that the largest index inthe current CU is N (e.g., index value is chosen from {0, 1, 2, . . . ,N}, inclusively, then the number of bins to code each index can be └log₂(N+1)┘┘ or ┌ log₂(N+1)┐, if these two values are not equal. As theescape pixel is assigned the largest index (e.g., after all the pixelvalues in the palette are assigned their index values), coding theescape pixel takes ┌ log₂(N+1)┐ bins.

In some cases, by exploiting dependencies, such as the methods describedabove, the largest symbol value for the current index may be reduced byone. In other words, the escape pixel may take ┌ log₂ N┐ or ┌ log₂(N+1)┐bins depending on whether the redundancy removal condition is enabled ornot. As a result, the decoder may first need to calculate whether thelargest index symbol value is N or N−1 to determine how many bins areneed to decode the index. This introduced additional on chip delay andhas negative effect to the decoder pipelining. In some embodiments, inorder to remove this delay and any negative effects on the decoderpipelining, this redundancy removal mechanism may be restricted. Forexample, the maximum number of bins used for index coding may be set toa constant. In one example, the escape pixel's index value may alwaysuse ceil(log 2(N+1)) bins. In another example, if ceil(log 2(N+1)) isequal to ceil(log 2(N)), the redundancy removal procedure for escapepixels is enabled, and otherwise, the redundancy removal procedure forescape pixels is disabled.

Encoder Side Flowchart

FIG. 9 is a flowchart illustrating a method 900 for encoding video datain a bitstream in accordance with aspects of the present disclosure. Forexample, the video data may be non-natural video data that includescomputer-generated screen contents. The steps illustrated in FIG. 9 maybe performed by a video encoder (e.g., the video encoder 20) or anyother component. For convenience, method 900 is described as performedby a video coder (also simply referred to as coder), which may be thevideo encoder 20 or another component.

The method 900 begins at block 901. At block 905, the coder analyzes aplurality of pixels in a coding unit (CU). Each pixel in the CU may beassociated with a pixel value. For example, multiple pixels in the CUmay have the same pixel value.

At block 910, the coder generates a palette based on the plurality ofpixels in the CU. The palette may include a plurality of palette entriesthat are each associated with an index value and a pixel valueassociated with the index value. An example of the palette isillustrated in FIG. 4.

At block 915, the coder determines one or more run lengths associatedwith the CU. As described above, each run length indicates the number ofconsecutive positions, starting from and including a current position inthe CU, that are associated with a copy-left mode or a copy-above mode.

At block 920, the coder determines one or more index values associatedwith the CU. As described above, each index value indicates a pixelvalue in the palette that is associated with the current position in theCU. In the example of FIG. 4, an index value of 0 indicates that thecurrent position in the CU has a white pixel value, and an index valueof 1 indicates that the current position in the CU has a grey pixelvalue.

At block 925, the coder determines one or more escape pixel valuesassociated with the CU. As described above, each escape pixel valueindicates a pixel value that is not in the palette associated with theCU. In the example of FIG. 4, the two positions in the CU having blackpixel values are coded in escape mode and the coder signals the blackpixel values in the bitstream as escape pixel values.

At block 930, the coder encodes the CU based on the generated palette,determined run lengths, determined index values, and determined escapepixel values. In some embodiments, the escape pixel values are encodedin consecutive positions in the bitstream (e.g., at the end of theportion of the bitstream associated with the CU). For example, theconsecutive positions of the escape pixel values appear in the bitstreamafter all the run lengths and index values associated with the CU. Insuch embodiments, after all the run lengths and the index values havebeen parsed by a decoder, the escape pixel values can be processed(e.g., parsed) in parallel. The method ends at block 935.

In the method 900, one or more of the blocks shown in FIG. 9 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. In some embodiments, additional blocks may beadded to the method 900. The embodiments of the present disclosure arenot limited to or by the example shown in FIG. 9, and other variationsmay be implemented without departing from the spirit of this disclosure.

Other Considerations

Information and signals disclosed herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative logical blocks, and algorithm steps describedin connection with the embodiments disclosed herein may be implementedas electronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Such techniques may beimplemented in any of a variety of devices such as general purposescomputers, wireless communication device handsets, or integrated circuitdevices having multiple uses including application in wirelesscommunication device handsets and other devices. Any features describedas devices or components may be implemented together in an integratedlogic device or separately as discrete but interoperable logic devices.If implemented in software, the techniques may be realized at least inpart by a computer-readable data storage medium comprising program codeincluding instructions that, when executed, performs one or more of themethods described above. The computer-readable data storage medium mayform part of a computer program product, which may include packagingmaterials. The computer-readable medium may comprise memory or datastorage media, such as random access memory (RAM) such as synchronousdynamic random access memory (SDRAM), read-only memory (ROM),non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The techniques additionally,or alternatively, may be realized at least in part by acomputer-readable communication medium that carries or communicatesprogram code in the form of instructions or data structures and that canbe accessed, read, and/or executed by a computer, such as propagatedsignals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor.” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software or hardware configured for encoding and decoding, orincorporated in a combined video encoder-decoder (CODEC). Also, thetechniques could be fully implemented in one or more circuits or logicelements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components, orunits are described in this disclosure to emphasize functional aspectsof devices configured to perform the disclosed techniques, but do notnecessarily require realization by different hardware units. Rather, asdescribed above, various units may be combined in a codec hardware unitor provided by a collection of inter-operative hardware units, includingone or more processors as described above, in conjunction with suitablesoftware and/or firmware.

Although the foregoing has been described in connection with variousdifferent embodiments, features or elements from one embodiment may becombined with other embodiments without departing from the teachings ofthis disclosure. However, the combinations of features between therespective embodiments are not necessarily limited thereto. Variousembodiments of the disclosure have been described. These and otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A method for decoding video data provided in abitstream, the bitstream including a coding unit (CU) coded in palettemode, the method comprising: parsing a palette associated with the CUprovided in the bitstream, the palette including a plurality of paletteentries that are each associated with an index value and a pixel valueassociated with the index value; parsing one or more run lengthsprovided in the bitstream that are associated with the CU, each runlength indicating a number of consecutive positions, starting from andincluding a current position in the CU, that are associated with acopy-left mode or a copy-above mode; parsing one or more index valuesprovided in the bitstream that associated with the CU, each index valueindicating a pixel value in the palette that is associated with thecurrent position in the CU; parsing one or more escape pixel valuesprovided in the bitstream that are associated with the CU, each escapepixel value indicating a pixel value that is not in the palette, whereinthe escape pixel values are parsed from consecutive positions in thebitstream, the consecutive positions being in the bitstream after all ofthe run lengths and the index values associated with the CU; anddecoding the CU based on the parsed palette, parsed run lengths, parsedindex values, and parsed escape values.
 2. The method of claim 1,further comprising resetting an arithmetic coding variable specifying arange of a current interval associated with the CU after parsing all ofthe run lengths and the index values associated with the CU.
 3. Themethod of claim 1, wherein the escape pixel values associated with theCU are parsed in parallel after parsing all of the run lengths and theindex values associated with the CU.
 4. The method of claim 1, whereinthe index values are parsed from the consecutive positions in thebitstream that are before the escape pixel values associated with the CUbut after all the run lengths associated with the CU.
 5. The method ofclaim 4, further comprising resetting an arithmetic coding variablespecifying a range of a current interval associated with the CU afterparsing all of the run lengths and the index values associated with theCU.
 6. The method of claim 4, wherein the index values associated withthe CU are parsed in parallel after parsing all of the run lengthsassociated with the CU.
 7. The method of claim 1, further comprising:determining that a first position in the CU that immediately precedesthe current position is associated with an end of a copy-above run; andin response to determining that the first position in the CU isassociated with an end of a copy-above run, determining an index valueassociated with the current position without determining whether asecond position immediately above the current position in the CU isassociated with an escape pixel value.
 8. The method of claim 1, whereinthe CU includes one of a copy-above run or a copy-left run that includesan escape pixel value.
 9. An apparatus for decoding video data providedin a bitstream, comprising: a memory configured to store video dataassociated with the bitstream, the bitstream including a coding unit(CU) coded in palette mode; and a processor in communication with thememory and configured to: parse a palette associated with the CUprovided in the bitstream, the palette including a plurality of paletteentries that are each associated with an index value and a pixel valueassociated with the index value; parse one or more run lengths providedin the bitstream that are associated with the CU, each run lengthindicating a number of consecutive positions, starting from andincluding a current position in the CU, that are associated with acopy-left mode or a copy-above mode; parse one or more index valuesprovided in the bitstream that associated with the CU, each index valueindicating a pixel value in the palette that is associated with thecurrent position in the CU; parse one or more escape pixel valuesprovided in the bitstream that are associated with the CU, each escapepixel value indicating a pixel value that is not in the palette, whereinthe escape pixel values are parsed from consecutive positions in thebitstream, the consecutive positions being in the bitstream after all ofthe run lengths and the index values associated with the CU; and decodethe CU based on the parsed palette, parsed run lengths, parsed indexvalues, and parsed escape values.
 10. The apparatus of claim 9, whereinthe processor is further configured to reset an arithmetic codingvariable specifying a range of a current interval associated with the CUafter parsing all of the run lengths and the index values associatedwith the CU.
 11. The method of claim 9, wherein the processor isconfigured to parse the escape pixel values associated with the CU inparallel after parsing all of the run lengths and the index valuesassociated with the CU.
 12. The method of claim 9, wherein the processoris configured to parse the index values from the consecutive positionsin the bitstream that are before the escape pixel values associated withthe CU but after all the run lengths associated with the CU.
 13. Themethod of claim 12, wherein the processor is further configured to resetan arithmetic coding variable specifying a range of a current intervalassociated with the CU after parsing all of the run lengths and theindex values associated with the CU.
 14. The method of claim 12, whereinthe processor is configured to parse the index values associated withthe CU in parallel after parsing all of the run lengths associated withthe CU.
 15. The method of claim 9, wherein the processor is furtherconfigured to: determine that a first position in the CU thatimmediately precedes the current position is associated with an end of acopy-above run; and in response to determining that the first positionin the CU is associated with an end of a copy-above run, determine anindex value associated with the current position without determiningwhether a second position immediately above the current position in theCU is associated with an escape pixel value.
 16. The method of claim 9,wherein the CU includes one of a copy-above run or a copy-left run thatincludes an escape pixel value.
 17. A method for encoding video data ina bitstream, comprising: analyzing a plurality of pixels in a codingunit (CU), each pixel having a pixel value associated therewith;generating a palette based on the plurality of pixels in the CU, thepalette including a plurality of palette entries that are eachassociated with an index value and a pixel value associated with theindex value; determining one or more run lengths associated with the CUin the bitstream, each run length indicating a number of consecutivepositions, starting from and including a current position in the CU,that are associated with a copy-left mode or a copy-above mode;determining one or more index values associated with the CU in thebitstream, each index value indicating a pixel value in the palette thatis associated with the current position in the CU; determining one ormore escape pixel values associated with the CU in the bitstream, eachescape pixel value indicating a pixel value that is not in the palette;and encoding the CU based on the generated palette, determined runlengths, determined index values, and determined escape pixel values,wherein the escape pixel values are encoded in consecutive positions inthe bitstream, the consecutive positions being in the bitstream afterall of the run lengths and the index values associated with the CU. 18.The method of claim 17, wherein the index values are encoded inconsecutive positions in the bitstream, the consecutive positions beingin the bitstream before the escape pixel values associated with the CUbut after all the run lengths associated with the CU.
 19. The method ofclaim 17, further comprising: determining that a first position in theCU that immediately precedes the current position is associated with anend of a copy-above run; and in response to determining that the firstposition in the CU is associated with an end of a copy-above run,determining an index value associated with the current position withoutdetermining whether a second position immediately above the currentposition in the CU is associated with an escape pixel value.
 20. Themethod of claim 17, wherein the CU includes one of a copy-above run or acopy-left run that includes an escape pixel value.
 21. The method ofclaim 17, further comprising determining a first offset indicating aposition in the bitstream that corresponds to an index value having anearliest position among the index values associated with the CU.
 22. Themethod of claim 17, further comprising determining a second offsetindicating a position in the bitstream that corresponds to an escapepixel value having an earliest position among the escape pixel valuesassociated with the CU.
 23. An apparatus for encoding video data in abitstream, comprising: a memory configured to store video dataassociated with the bitstream, the bitstream including a coding unit(CU) coded in palette mode; and a processor in communication with thememory and configured to: analyze a plurality of pixels in a coding unit(CU), each pixel having a pixel value associated therewith; generate apalette based on the plurality of pixels in the CU, the paletteincluding a plurality of palette entries that are each associated withan index value and a pixel value associated with the index value;determine one or more run lengths associated with the CU in thebitstream, each run length indicating a number of consecutive positions,starting from and including a current position in the CU, that areassociated with a copy-left mode or a copy-above mode; determine one ormore index values associated with the CU in the bitstream, each indexvalue indicating a pixel value in the palette that is associated withthe current position in the CU; determine one or more escape pixelvalues associated with the CU in the bitstream, each escape pixel valueindicating a pixel value that is not in the palette; and encode the CUbased on the generated palette, determined run lengths, determined indexvalues, and determined escape pixel values, wherein the escape pixelvalues are encoded in consecutive positions in the bitstream, theconsecutive positions being in the bitstream after all of the runlengths and the index values associated with the CU.
 24. The apparatusof claim 23, wherein the processor is configured to encode the indexvalues in consecutive positions in the bitstream, the consecutivepositions being in the bitstream before the escape pixel valuesassociated with the CU but after all the run lengths associated with theCU.
 25. The apparatus of claim 23, wherein the processor is furtherconfigured to: determine that a first position in the CU thatimmediately precedes the current position is associated with an end of acopy-above run; and in response to determining that the first positionin the CU is associated with an end of a copy-above run, determine anindex value associated with the current position without determiningwhether a second position immediately above the current position in theCU is associated with an escape pixel value.
 26. The apparatus of claim23, wherein the CU includes one of a copy-above run or a copy-left runthat includes an escape pixel value.
 27. The apparatus of claim 23,wherein the processor is further configured to determine a first offsetindicating a position in the bitstream that corresponds to an indexvalue having an earliest position among the index values associated withthe CU.
 28. The apparatus of claim 23, further comprising determining asecond offset indicating a position in the bitstream that corresponds toan escape pixel value having an earliest position among the escape pixelvalues associated with the CU.